This application is based on Japanese Patent Application No. 11-288034 filed October 8, the contents of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates in general to a hybrid-vehicle drive system, particularly to a hybrid-vehicle drive system having an engine and an electric motor which are mechanically connected to each other by a planetary gear device, and more particularly to a control when the vehicle drive mode is switched from a motor-drive mode to an engine-drive mode.
2. Discussion of Related Art
There is known a drive system for a hybrid automotive vehicle, which includes (a) an engine operated by combustion of a fuel to produce a drive force, (b) an electric motor, (c) an output member operatively connected to drive wheels, (d) a planetary gear device associated with the engine, electric motor and output member, for synthesizing and distributing a drive force or forces, and (e) a plurality of frictional coupling devices such as clutches and brakes for selectively connecting and disconnecting rotary elements of the planetary gear device to and from each other or a stationary member. An example of such a hybrid vehicle drive system is disclosed in JP-A-9-37411, wherein various vehicle drive modes are selectively established for driving the vehicle, by controlling the operating states of the clutches and brakes. For instance, the drive modes include a motor-drive mode in which the vehicle is driven by the electric motor as a drive power source, and an engine-drive mode in which the vehicle is driven by the engine as the vehicle drive source.
A hybrid-vehicle drive system as described above is not necessarily satisfactory in the manner of control in which the vehicle-drive is switched from the motor-drive mode to the engine-drive mode, when the clutch is engaged while the operating speed of the engine is relatively low. Namely, the known hybrid-vehicle drive system suffers from a reduced vehicle drive force when the clutch is engaged at a relatively low speed of the engine, for switching the vehicle drive mode from the motor-drive mode to the engine-drive mode.
It is therefore an object of the present invention to provide a hybrid-vehicle drive system which is improved in the manner of control in which the vehicle drive mode is switched from the motor-drive mode to the engine-drive mode.
The above object may be achieved according to a first aspect of the present invention, which provides a hybrid-vehicle drive system, A hybrid drive system for an automotive vehicle, comprising: (a) an engine operable by combustion of a fuel to generate a drive force; (b) an electric motor; (c) an output member operatively connected to a drive wheel of the vehicle for driving the vehicle; (d) a planetary gear device having a first rotary element connected to the engine, a second rotary element connected to the electric motor, and a third rotary element; (e) a first clutch through which the second rotary member is connected to the output member; (f) a second clutch through which the third rotary member is connected to the output member; (g) forward-motor-drive control means for engaging the first clutch and releasing the second clutch to thereby establish a forward motor drive mode in which the automotive vehicle is driven in a forward direction by operation of the electric motor while the engine is at rest: (h) forward-engine-drive control means for engaging at least the second clutch to establish an engine-drive mode in which the automotive vehicle is driven in the forward direction by operation of the engine; and (i) second-clutch control means operable upon switching of a vehicle drive mode from the forward motor drive mode to the forward engine drive mode, for engaging the second clutch only after an operating speed of the engine has exceeded an operating speed of the electric motor.
In the hybrid drive system constructed according to the first aspect of this invention described above, the second-clutch control means is operated upon switching of the vehicle drive mode from the forward motor drive mode (established by the forward-motor-drive control means) to the engine drive mode (established by the forward-engine-drive control means). The second-clutch control means is arranged to engage the second clutch only after the operating speed of the engine has exceeded that of the electric motor. This arrangement permits a smooth transition of the vehicle drive mode to the engine drive mode, for thereby rapidly increasing the vehicle drive force, without a reduction of the vehicle drive force during the transition, where the transition to the engine drive mode is required due to an increase in the operating amount of the accelerator pedal, for example. That is, if the second clutch were engaged while the engine speed is lower than the motor speed, the vehicle drive force would be partly consumed by an increase of the engine speed to the motor speed.
In one preferred form of the hybrid drive system according to the first aspect of the invention described above, the second clutch is a hydraulically operated frictional coupling device capable of effecting a slipping engagement, and the second-clutch control means is adapted to initiate a gradual increase of a hydraulic pressure to be applied to the second clutch for engaging the second clutch, when the operating speed of the engine has exceeded the operating speed of the electric motor.
In another preferred form of the hybrid drive system described above, the electric motor consists of a motor/generator, and the planetary gear device is a double-pinion type planetary gear device having a sun gear as the first rotary element, a carrier as the second rotary element, and a ring gear as the third rotary element. In this instance, the sun gear is connected to the engine, while the carrier is connected to the motor/generator, and is further connected through the first clutch to the output member. Further, the ring gear is connected through the second clutch to the output member. For example, the output member may be an input shaft of an automatic transmission, which is preferably a continuously variable transmission of belt-and-pulley type. The planetary gear device may be of a single-pinion type, and the transmission may be a continuously variable transmission of other types such as toroidal type.
The motor/generator indicated above selectively functions as an electric generator as well as an electric motor. Preferably, the motor/generator is operated as the electric motor serving as a vehicle drive power source, and as the electric generator for applying a regenerative brake to the vehicle and generating an electric energy for charging an electric energy storing device, for instance. The motor/generator may be used as an electric motor only. The hybrid drive system may use both an electric motor and an electric generator as two separate units, or two separate motor/generators.
Each of the first and second clutches indicated above may be a hydraulically operated friction clutch of a single-disc type or multiple-disc type, which is frictionally engaged by a suitable hydraulic actuator such as a hydraulic cylinder. Alternatively, the first and second clutches may be electromagnetic clutches. At least one additional clutch and/or brake may be used in addition to the first and second clutches, as needed.
In the hybrid drive system wherein the second clutch is engaged only after the engine speed has exceeded the motor speed, the determination as to whether the engine speed has exceeded the motor speed may be effected by directly comparing these two speeds, or by comparing the operating speeds of selected two rotary elements of the planetary gear device. For instance, the planetary gear device having a first, a second and a third rotary element may be arranged such that when the speed of the first rotary element becomes higher than that of the second rotary element, the speed of the third rotary element becomes higher than that of the secondary rotary element. In this instance, the determination as to whether the engine speed has exceeded the motor speed may be effected by determining whether the speed of the first or third rotary element has exceeded the speed of the second rotary element as a result of an increase of the engine speed. In this case, the second clutch is engaged when the speed of the first or third rotary element has exceeded that of the second rotary element.
In a further preferred form of the hybrid drive system according to the first aspect of this invention, the second clutch is a hydraulically operated frictional coupling device capable of effecting a slipping engagement, the hybrid drive system further comprising: first engine starting means for cranking the engine with a starter, and thereby starting the engine: second engine-starting means for cranking the engine by slipping engagement of the second clutch, and thereby starting the engine; and engine-starting-means changing means for starting the engine by the second engine-starting means when the engine cannot be started by the first engine-starting means.
The hybrid drive system according to the above preferred form has two engine-starting means, namely, the first engine-starting means using the starter and the second engine-starting means using the second clutch. If the engine cannot be started by cranking with the starter under the control of the first engine-starting means, the engine is started by cranking with a slipping engagement of the second clutch under the control of the second engine-starting means. In this form of the invention, the engine can be started to drive the vehicle in the engine drive mode by operation of the engine, even in the event of a failure of the engine starter,
The hybrid drive system according to the first aspect of the invention need not be provided with any engine starting means such as the first engine-starting means and second engine-starting means described above, or non-cranking engine-starting means which will be described. Further, the hybrid drive system according to the first aspect of the invention may be provided with any other engine-starting means. When two or more different engine-starting means are provided, the second-clutch control means is preferably activated irrespective of the type of the engine-starting means used to start the engine. However, the second-clutch control means may be activated only when the engine is started with a selected one or ones of the plurality of engine-starting means, which assure or assures a high response in the control of transition from the forward motor drive mode to the engine drive mode under. The second engine-starting means is preferably activated only when the speed of the electric motor is higher than a predetermined lower limit (above which the engine can be operated by combustion of a fuel).
The object indicated above may also be achieved according to a second aspect of the present invention, which provides a hybrid drive system for an automotive vehicle, comprising: (a) an engine operable by combustion of a fuel to generate a drive force; (b) an electric motor; (c) an output member operatively connected to a drive wheel of the vehicle for driving the vehicle; (d) a planetary gear device having a first rotary element connected to the engine, a second rotary element connected to the electric motor, and a third rotary element; (e) a first clutch through which the second rotary member is connected to the output member; (f) a second clutch through which the third rotary member is connected to the output member; (g) forward-motor-drive control means for engaging the first clutch and releasing the second clutch to thereby establish a forward motor drive mode in which the automotive vehicle is driven in a forward direction by operation of the electric motor while the engine is at rest; (h) forward-engine-drive control means for engaging both of the first clutch and the second clutch to establish a direct engine drive mode in which the automotive vehicle is driven in the forward direction by operation of the engine, with the planetary gear device being rotated as a unit, and for releasing the first clutch and engaging the second clutch to establish an engine-and-motor drive mode in which the automotive vehicle is driven in the forward direction by operations of both of the engine and the electric motor; and (i) mode selecting means operable upon switching of a vehicle drive mode from the forward motor drive mode to one of the direct engine drive mode and the engine-and-motor drive mode, for determining whether the engine is likely to stall if the direct engine drive mode is established, and commanding the forward-engine-drive control means to establish the engine-and-motor drive mode, when it is determined that the engine is likely to stall if the direct engine drive mode is established.
In the hybrid drive system constructed according to the second aspect of this invention described above, the mode selecting means is operated when the vehicle drive mode is switched from the forward motor drive mode (established by the forward-motor-drive control means) to one of the direct engine drive mode and the engine-and-motor drive mode (to be established by the forward-engine-drive control means). The mode selecting means is arranged to determine whether the engine is likely to stall if the direct engine drive mode is established. When it is determined that the engine is likely to stall, the mode selecting means commands the forward-engine-drive control means to establish the engine-and-motor drive mode. This arrangement permits the vehicle to be driven in the engine-and-motor drive mode with a sufficiently large drive force, without a risk of stalling of the engine, since the direct motor drive mode is not established if the engine stall is expected, even when the vehicle drive mode from the forward motor drive mode to the direct engine is required. In the engine-and-motor drive mode, the vehicle can be driven even with the engine being operated as a drive power source at a comparatively low speed lower than its idling speed.
The hybrid drive system according to the second aspect of this invention described above may use a double-pinion or single-pinion type planetary gear device having a sun gear, a carrier and a ring gear as the respective first, second and third rotary elements, and may use a continuously variable transmission of various types, as described above with respect to the first aspect of the invention. Further, the present hybrid drive system may use at least one motor/generator each selectively functioning as an electric motor and an electric generator.
In the engine-and-motor drive mode selected by the mode selecting means according to the second aspect of the invention, it is desirable that the states of connections of the planetary gear device to the electric motor and the engine and the gear ratio of the planetary gear device be determined so that the load torque of the electric motor is smaller than that of the engine and so that the torque acting on the output member in a steady running state of the vehicle is equal to a sum of the torques of the electric motor and the engine. This desirability is also applicable to any other hybrid drive system which has the engine-and-motor drive mode and which will be described.
The determination by the mode selecting means as to whether the engine is likely to stall if the direct engine drive mode is established may be effected in various manners. For instance, the mode selecting means monitors the engine speed when the vehicle drive mode is required to be switched to the direct engine drive mode, and determine whether the engine speed has been lowered below a predetermined threshold value, as a result of an engagement of the second clutch. The mode selecting means determines that the engine is likely to stall, if the monitored engine speed has been lowered below the threshold value. Alternatively, the determination may be effected on the basis of the speed of the output member which is detected at a predetermined point of time during an engaging action of the second clutch, for example, when the engine speed begins to be reduced.
The object indicated above may also be achieved according to a third aspect of the present invention, which provides a hybrid drive system for an automotive vehicle, the hybrid drive system comprising: a vehicle drive power source including an engine operable by combustion of a fuel to generate a drive force, and an electric motor; and non-cranking engine starting means operable upon switching of a vehicle drive mode from a forward motor drive mode in which the automotive vehicle is driven by operation of the electric motor only, to an engine drive mode in which the automotive vehicle is driven by operation of the engine, the non-cranking engine starting means starting the engine by merely controlling the starting of the engine without cranking of the engine, when an operating speed of the engine is higher than a predetermined threshold, the controlling the starting of the engine comprising controlling a state in which the fuel is injected into the engine.
In the hybrid drive system constructed according to the third aspect of this invention described above, the non-cranking engine starting means is operated when the vehicle drive mode is required to be changed from the motor drive mode to the engine drive mode. The non-cranking engine starting means is arranged to start the engine by merely controlling the fuel injecting state of the engine and other states of the starting of the engine, without cranking the engine, when the engine speed is higher than the predetermined threshold. Where the operating amount of the accelerator pedal is increased immediately after the vehicle drive mode has been changed from the engine drive mode to the motor drive mode, for instance, the vehicle drive mode is required to be changed to the engine drive mode again. In this case, the engine is started without cranking, so that the transition to the engine drive mode can be rapidly achieved. Where the engine is started by cranking with an engine starter, the pinion of the starter must be brought into meshing engagement with the ring gear provided on the flywheel of the engine, so that the pinion cannot be held in meshing engagement with the ring gear until the engine speed has been lowered to a predetermined value. Accordingly, the starting of the engine and the transition to the engine drive mode are delayed. This delay is not encountered according to the third aspect of this invention.
The hybrid drive system according to the third aspect of this invention described above may use a double-pinion or single-pinion type planetary gear device having a sun gear, a carrier and a ring gear as the respective first, second and third rotary elements, and may use a continuously variable transmission of various types, as described above with respect to the first aspect of the invention. Further, the present hybrid drive system may use at least one motor/generator each selectively functioning as an electric motor and an electric generator.
In the hybrid drive system according to the third aspect of the invention, the vehicle is driven in the engine drive mode, by operation of the engine only, or by operations of both of the engine and the electric motor, namely, in the direct engine drive mode or in the engine-and-motor drive mode, for example, as described above with respect to the second aspect of the invention.
The hybrid drive system according to one preferred form of this third aspect of the invention further comprises (a) an output member operatively connected to a drive wheel of the vehicle, (b) a planetary gear device having a first rotary element connected to the engine, a second rotary element connected to the electric motor and connected to the output member through a first clutch, and a third rotary element connected to the output member through a second clutch, (c) forward-motor-drive control means for engaging the first clutch and releasing the second clutch, to thereby establish the forward motor drive mode in which the automotive vehicle is driven in a forward direction by operation of the electric motor while the engine is at rest, and (d) forward-engine-drive control means for engaging at least the second clutch, to thereby establish the engine drive mode in which the automotive vehicle is driven in the forward direction by operation of the engine.
The object indicated above may also be achieved according to a fourth aspect of this invention, which provides a hybrid drive system for an automotive vehicle, comprising:
(a) a vehicle drive power source including an engine operable by combustion of a fuel to generate a drive force, and an electric motor;
(b) a transmission;
(c) a clutch of a frictional coupling type disposed between the engine and the transmission;
(d) clutch-slip control means operable upon switching of a vehicle drive mode from a motor drive mode in which the automotive vehicle is driven by operation of the electric motor only, to an engine drive mode in which the automotive vehicle is driven by operation of the engine, the clutch-slip control means effecting a slipping engagement of the clutch; and
(e) transition-input-torque estimating means for estimating an input torque of the transmission on the basis of an engaging torque of the clutch during the slipping engagement of the clutch while the vehicle drive mode is switched from the motor drive mode to the engine drive mode.
In the hybrid drive system constructed according to the fourth aspect of this invention described above, the clutch-slip control means is operated upon switching of the vehicle drive mode from the motor drive mode to the engine drive mode. The clutch-slip control means is adapted to effect a slipping engagement of the clutch disposed between the engine and the transmission. At the same time, the transition-input-torque estimating means is operated to estimate the input torque of the transmission on the basis of the engaging torque (transmission torque capacity) during the slipping engagement of the clutch. This arrangement permits the input torque of the transmission to be estimated with high accuracy while the vehicle drive mode is switched from the motor drive mode to the engine drive mode. Based on the highly accurately estimated input torque of the transmission, the hydraulic pressures for controlling the transmission can be controlled with accordingly high accuracy. Generally, a desired hydraulic pressure to be applied to each hydraulically operated portion of a transmission is calculated on the basis of the drive torque generated by the vehicle drive source, the inertia of each rotary member, the torque of a torque converter, and other parameters associated with the transmission. Where the slipping amount of the clutch between the engine and the transmission is controlled upon switching of the vehicle drive mode (upon switching of the vehicle drive power source), a clutch or brake device incorporated in the transmission or a belt of a belt-and-pulley type continuously variable transmission would undesirably suffer from slipping due to an excessive amount of the input torque of the transmission if the engaging torque of the clutch between the engine and the transmission were not taken into account in calculating the desired hydraulic pressure. This problem can be avoided according to the fourth aspect of the invention described above.
The hybrid drive system according to the fourth aspect of this invention described above may use a double-pinion or single-pinion type planetary gear device having a sun gear, a carrier and a ring gear as the respective first, second and third rotary elements, and may use a continuously variable transmission of various types, as described above with respect to the first aspect of the invention. Further, the present hybrid drive system may use at least one motor/generator each selectively functioning as an electric motor and an electric generator.
In the hybrid drive system according to the fourth aspect of the invention, the vehicle is driven in the engine drive mode, by operation of the engine only, or by operations of both of the engine and the electric motor, namely, in the direct engine drive mode or in the engine-and-motor drive mode, for example, as described above with respect to the second aspect of the invention.
The clutch disposed between the engine and the transmission may be a hydraulically operated friction clutch of a single-disc type or multiple-disc type, which is frictionally engaged by a suitable hydraulic actuator such as a hydraulic cylinder. Alternatively, the clutch may be electromagnetic clutches. At least one additional clutch and/or brake may be used in addition to the first and second clutches, as needed.
The hybrid drive system according to one preferred form of this fourth aspect of the invention further comprises (a) an output member operatively connected to a drive wheel of the vehicle, (b) a planetary gear device having a first rotary element connected to the engine, a second rotary element connected to the electric motor and connected to the output member through a first clutch, and a third rotary element connected to the output member through a second clutch, (c) forward-motor-drive control means for engaging the first clutch and releasing the second clutch, to thereby establish the forward motor drive mode in which the automotive vehicle is driven in a forward direction by operation of the electric motor while the engine is at rest, and (d) forward-engine-drive control means for engaging at least the second clutch, to thereby establish the engine drive mode in which the automotive vehicle is driven in the forward direction by operation of the engine. Further, the second clutch is a frictional coupling clutch capable of effecting a slipping engagement and the output member is connected to the transmission.
The object indicated above may also be achieved according to a fifth aspect of this invention, which provides a hybrid drive system for an automotive vehicle, comprising:
(a) an engine operable by combustion of a fuel to generate a drive force;
(b) an electric motor;
(c) an output member operatively connected to a drive wheel of the vehicle for driving the vehicle;
(d) a planetary gear device having a first rotary element connected to the engine, a second rotary element connected to the electric motor, and a third rotary element;
(e) a first clutch through which the second rotary element is connected to the output member;
(f) a second clutch through which the third rotary member is connected to the output member;
(g) forward-motor-drive control means for engaging the first clutch and releasing the second clutch, to thereby establish a forward motor drive mode in which the automotive vehicle is driven in a forward direction by operation of the electric motor while the engine is at rest;
(h) forward-engine-drive control means for releasing the first clutch and engaging the second clutch, to thereby establish an engine-and-motor drive mode in which the automotive vehicle is driven in the forward direction by operations of both of the engine and the electric motor;
(i) the first clutch being a frictionally coupling clutch; and
(j) first-clutch-releasing stand-by means operable upon switching of a vehicle drive mode from the forward motor drive mode to the engine-and-motor drive mode, the first-clutch-releasing stand-by means reducing an engaging torque of the first clutch to a value not causing slipping of the first clutch, before the first clutch is released.
In the hybrid drive system constructed according to the fifth aspect of the present invention, the first-clutch-releasing stand-by means is operated upon switching of the vehicle drive mode from the forward motor drive mode to the engine-and-motor drive mode. The first-clutch-releasing stand-by means is adapted to reduce the engaging torque of the first clutch to a value not causing slipping of the first clutch, prior to the releasing of the first clutch. This arrangement permits an excellent response when the first clutch is released when a predetermined condition is satisfied, so that the transition to the engine-and-motor drive mode is facilitated, without a variation in the vehicle drive force due to a delayed response, and without a risk of stalling of the engine.
The object indicated above may also be achieved according to a sixth aspect of this invention, which provides a hybrid drive system for an automotive vehicle, comprising:
(a) an engine operable by combustion of a fuel to generate a drive force;
(b) an electric motor;
(c) an output member operatively connected to a drive wheel of the vehicle for driving the vehicle;
(d) a planetary gear device having a first rotary element connected to the engine, a second rotary element connected to the electric motor, and a third rotary element;
(e) a first clutch through which the second rotary element is connected to the output member;
(f) a second clutch through which the third rotary member is connected to the output member;
(g) forward-motor-drive control means for engaging the first clutch and releasing the second clutch, to thereby establish a forward motor drive mode in which the automotive vehicle is driven in a forward direction by operation of the electric motor while the engine is at rest;
(h) forward-engine-drive control means for releasing the first clutch and engaging the second clutch, to thereby establish an engine-and-motor drive mode in which the automotive vehicle is driven in the forward direction by operations of both of the engine and the electric motor;
(i) the first clutch being a frictionally coupling clutch; and
(h) clutch control means operable upon switching of a vehicle drive mode from the forward motor drive mode to the engine-and-motor drive mode, the clutch control means gradually reducing an engaging torque of the second clutch, and releasing the first clutch when a torque of the electric motor and the engaging torque of the second clutch have satisfied a predetermined relationship representative of a ratio of the torque of the electric motor and the engaging torque of the second clutch with respect to each other, which relationship is suitable for driving the vehicle in the engine-and-motor drive mode.
In the hybrid drive system constructed according to the sixth aspect of the invention described above, the clutch control means is operated when the vehicle drive mode is switched from the motor drive mode to the engine-and-motor drive mode. The clutch control means is arranged to gradually increase the engaging torque of the second clutch, and release the first clutch when the motor torque and the engaging torque of the second clutch have satisfied a predetermined relationship representative of the ratio of the motor torque and the engaging torque of the second clutch with respect to each other in the engine-and-motor drive mode. This arrangement facilitates the transition to the engine-and-motor drive mode with a reduced variation in the vehicle drive force upon releasing of the first clutch.
The hybrid drive systems according to the fifth and sixth aspects of this invention described above may also use a double-pinion or single-pinion type planetary gear device having a sun gear, a carrier and a ring gear as the respective first, second and third rotary elements, and may use a continuously variable transmission of various types, as described above with respect to the first aspect of the invention. Further, the present hybrid drive system may use at least one motor/generator each selectively functioning as an electric motor and an electric generator.